Currently lasers having energy outputs, high efficiency, high repetition rates and being tunable are in great demand for military, industrial and scientific applications. While process has been made in the development of a laser having such properties, none has been found which answer all the these needs and operate in the near UV/visible/near IR region of the spectrum. Dyer lasers operating with improved laser dyes appear to offer some potential to meet the above requirements.
Ever since the lasing action of organic dyes was observed, intense efforts have been made to develop this field. The main reasons for this development have been the unique feature of dye laser to be tunable over a wide range of wavelengths. In addition, other advantages of dye lasers include the fact that dye lasers are liquid lasers and, hence, have a high optical quality of the active medium is implied and a high pulse repetition rate is possible because of the simplicity of cooling. Another advantage is that the cost preparing the active medium (the laser dye and solvent) is less than with solid state lasers. On the minus side however, laser dyes have demonstrated only moderator energies and a photodecomposition which limits their useful life. Another drawback to laser dyes is their requirement for an excitation flashlamp that has steep risetimes of about 1 microsecond and less to assure the laser action. As a consequence, flashlamps meeting this stringent requirement are difficult to build for operation above 500 Joules.
The present method of identifying organic dyes that have satisfactory laser action is largely one of trial and error. Thousands of organic compounds which show strong fluorescence have been synthesized and are commercially available. Fluorescence in this context is a spontaneous random emission. However, only a few show laser action, a coherent radiation, under flashlamp excitation. Most of the disadvantages in presently available laser dyes are closely related with the accumulation of dye molecules in their triplet state due to intersystem crossing. These triplet state molecules in turn absorb the laser light more or less efficiently depending on the magnitude of their triplet state absorption and concentration. Triplet-triplet (T-T) absorption is not very small in all laser dyes presently commercially available.
Thus, a continuing need exists in the state-of-the-art for new laser dyes with further reduced T-T absorption in which the lower laser action threshold makes it possible to employ commercial flashlamps with slower risetimes. More usable UV light is used thereby, to result in more efficient dye laser operation and a more efficient conversion of the pumping energy is provided due to a reduced T-T absorption. In addition, the need exist for a more photochemically stable laser dye to assure long term reliable operation.